I am a size 10/12 and normally get a large in a sweatshirt. If I want it oversized I order an XL. Once I read the reviews that suggested you size up, I ordered a xxl and it fits. Which is not the oversized look I was going for. I was very disappointed. I will say if you have boobs at all, you need to go up 2 sizes. I am a 38G (naturally) and the sweatshirt is too tight across my chest and this is with me going up 2 sizes.
The quality seems to be great but sizing is not.